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Optimizing myocardial supply/demand balance with alpha-adrenergic drugs during cardiopulmonary resuscitation
Insights
Alpha-adrenergic drugs improve coronary perfusion during cardiopulmonary resuscitation (CPR). Inotropic drugs may worsen myocardial ischemia by increasing oxygen demand and impeding blood flow.
Area of Science:
- Cardiology
- Cardiovascular Physiology
- Critical Care Medicine
Background:
- Myocardial blood supply and metabolic demands are critical during cardiopulmonary resuscitation (CPR).
- Assessing interventions to optimize coronary perfusion is essential for improving outcomes.
Purpose of the Study:
- To evaluate the effects of vasopressor infusion on myocardial blood supply and metabolic demands during CPR.
- To compare the impact of alpha-adrenergic (methoxamine) and inotropic (epinephrine) drugs on coronary perfusion and myocardial oxygen balance.
Main Methods:
- Studies were conducted in 14 dogs under steady-state conditions and during CPR with open-chest cardiac massage.
- Coronary diastolic blood pressure, coronary blood flow (CBF), and myocardial oxygen uptake were measured.
- Effects of methoxamine and epinephrine on hemodynamic parameters and subendocardial flow distribution were assessed.
Main Results:
- Vasopressor infusion (methoxamine or epinephrine) significantly increased diastolic blood pressure and coronary blood flow during CPR.
- Epinephrine increased myocardial oxygen uptake and "vigor of fibrillation" but reduced subendocardial blood flow.
- Methoxamine did not significantly alter intraventricular pressure, oxygen uptake, or coronary flow distribution.
Conclusions:
- Augmenting diastolic pressure with alpha-adrenergic drugs enhances coronary perfusion during CPR.
- Inotropic agents like epinephrine may exacerbate myocardial ischemia during CPR by increasing oxygen demand and impairing subendocardial blood supply.
Abstract:
In 14 dogs the determinants of myocardial blood supply and metabolic demands were assessed during cardiopulmonary resuscitation (CPR) and under steady-state conditions in fibrillating hearts on cardiopulmonary bypass. During open chest cardiac massage (nine dogs), coronary diastolic blood pressure and blood flow were low. Vasopressor infusion (methoxamine or epinephrine) raised diastolic pressure from 33 +/- 3 to 55 +/- 3 mm. Hg and increased coronary blood flow (CBF) 124 percent (from 38 +/- 3 to 85 +/- 11 c.c. per 100 Gm. per minute. Comparison of these drugs in fibrillating hearts on cardiopulmonary bypass showed that epinephrine increased the "vigor of fibrillation" (intraventricular balloon pressure rose 24 percent and oxygen uptake increased 42%) but impeded subendocardial flow 53% (endocardial/epicardial flow ratio fell from 0.79 to 0.48). In contrast, methoxamine did not significantly change intraventricular balloon pressure, oxygen uptake, coronary flow, or its distribution. We conclude that augmentation of diastolic pressure with alpha adrenergic drugs during CPR improves coronary perfusion and that inotropic drugs may worsen myocardial ischemia during CPR by raising oxygen demands while simultaneously impeding subendocardial blood supply.